The present invention relates to a magnetic data recording/reproducing device for recording and reproducing data on and from a disk-shaped magnetic recording medium through a magnetic head. More specifically, the present invention relates to a magnetic data recording/reproducing device comprising a linear motor for use in driving a carriage assembly having a magnetic head mounted thereon in a radial direction relative to a magnetic recording medium.
As well known in the art, flexible disk drives are a type of magnetic data recording/reproducing device on which a flexible disk can be mounted for the purpose of recording and reproducing data. Flexible disks have recently been increased in storage capacity. Typical flexible disks have a storage capacity of 1-2 megabytes (hereinafter, referred to as a normal capacity). There have been developed flexible disks with a storage capacity of 128 megabytes (hereinafter, referred to as a large capacity). In response to this, flexible disk drives have also been developed that can be used with a flexible disk of the large capacity.
The flexible disk drives used with a flexible disk of the normal capacity is different in mechanism from those used with a flexible disk of the large capacity. One of the differences lies in the structure of driving means for use in driving a carriage assembly having a magnetic head mounted thereon in a predetermined radial direction relative to a flexible disk mounted within the flexible disk drive. More specifically, the flexible disk drive for the normal-capacity flexible disk uses a stepping motor as the driving means. On the other hand, the flexible disk drive for the large-capacity flexible disk uses a linear motor as the driving means. Such a linear motor is called a voice coil motor.
The linear motor that is used as the driving means for the flexible disk drives used with the flexible disk of the large capacity will now be described. The linear motor comprises a pair of coils integrally assembled with the carriage assembly on both sides thereof, and a pair of magnetic circuit devices for generating a magnetic field in a direction intersecting that of an electric current flowing through the pair of coils.
Now, the description will be made with regard to one of the pair of magnetic circuit devices. The magnetic circuit device typically comprises a permanent magnet polarized along the thickness thereof and a yoke member. The yoke member comprises a center yoke which serves as a drive axis, a back yoke, and a pair of side yokes. The center yoke extends in the direction along which the carriage assembly moves and passes through the coil. The back yoke has a main surface extending in parallel with the center yoke at a certain distance and being opposed to the center yoke. The pair of side yokes are for magnetically connecting both ends of the center yoke with corresponding ends of the back yoke. The permanent magnet is fixed to the main surface of the back yoke. The center yoke, the back yoke, and the side yokes are each made of a steel plate having a thickness of at least 3 mm.
With this structure, by causing the electric current to flow through the coil in a direction intersecting that of the magnetic field generated by the magnetic circuit device, a drive force occurs in a direction extending to the drive axis on the basis of interaction of the electric current with the magnetic field. The drive force causes the linear motor to move the carriage assembly in the predetermined radial direction.
By the way, the pair of magnetic circuit devices should be mounted on a main substrate or plate of the flexible disk drive so as not to cause a positional deviation thereof. The pair of magnetic circuit devices have leakage flux because the permanent magnet is made of an advanced magnetic material. The leakage flux tends to adversely influence the magnetic head mounted on the carriage assembly.